Apparatus for drying a fibrous web

ABSTRACT

Disclosed is an apparatus for drying a fibrous web, in particular a paper web, paperboard web or tissue web, by way of hot air, on which the fibrous web is charged with the supply air for the drying from a supply air chamber and on which exhaust air from the drying operation passes into an exhaust air chamber, whereby the exhaust air from the exhaust air chamber is supplied at least partly to the suction side of a pressure booster and at least a part of the supply air from the pressure side of the pressure booster is supplied to the supply air chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for drying a fibrous web, inparticular a paper web, paperboard web or tissue web, by way of hot air.The invention relates in addition to a machine for producing a fibrousweb with a three-dimensional surface structure, said machine having sucha drying apparatus.

2. Description of the Related Art

On the known apparatuses of said type, the respective hot air dryingprocess involves a relatively high energy outlay.

What is needed in the art is an improved apparatus and an improvedmachine of the type initially referred to. More specifically, what isneeded is the apparatus and machine being optimized in particularinasmuch as the energy outlay required for the hot air drying process isreduced to a minimum.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for drying a fibrous web, inparticular a paper web, paperboard web or tissue web, by way of hot air,on which the fibrous web is charged with the supply air for the dryingfrom a supply air chamber and on which exhaust air from the dryingoperation passes into an exhaust air chamber, whereby the exhaust airfrom the exhaust air chamber is supplied at least partly to the suctionside of a pressure booster and at least a part of the supply air fromthe pressure side of the pressure booster is supplied to the supply airchamber.

The result, by virtue of this construction, is a hot air circuit onwhich the exhaust air from the drying operation is used, by which wayenergy is saved accordingly.

On a practical embodiment, the drying apparatus includes a so-calledimpingement drying device.

In this case the supply air chamber and the exhaust air chamber arearranged on the same side of the fibrous web.

The supply air chamber and the exhaust air chamber can form a sharedspace.

According to an advantageous alternative embodiment, the dryingapparatus includes a through-flow drying device.

In this case the supply air chamber and the exhaust air chamber can lieon opposite sides of the fibrous web.

In this case it is an advantage for a positive pressure in the rangefrom approximately 0 to approximately 0.5 bar and preferably in a rangefrom approximately 0.002 to approximately 0.3 bar to exist in the supplyair chamber.

Preferably a positive pressure ≧0.01, in particular ≧0.02 and preferably≧0.05 bar exists in the supply air chamber.

In addition it is an advantage for a negative pressure in a range fromapproximately 0 to approximately 0.8 bar and preferably in a range fromapproximately 0.2 to approximately 0.7 bar to exist in the exhaust airchamber.

Preferably a negative pressure in a range from approximately 0.4 toapproximately 0.7 exists in the exhaust air chamber.

According to a practical embodiment of the inventive drying apparatus,the pressure booster includes at least one blower, which can be forexample a multi-stage blower or a single-stage blower. Such a blower ofthe type in question is marketed under the name “Tubair”.

Advantageously it is also possible however for the pressure booster toinclude at least one radial blower and/or at least one axial blower.

The temperature of the supply air or supply air fraction originatingfrom the pressure booster is preferably ≧100° C., in particular ≧150° C.and preferably ≧200° C.

It is also an advantage in particular for the supply air chamber to besupplied with more than 50%, in particular more than 60%, in particularmore than 70% and preferably more than 80% of the supply air from thepressure side of the pressure booster.

According to an expedient practical embodiment of the inventive dryingapparatus, at least essentially 100% of the supply air from the pressureside of the pressure booster is supplied to the supply air chamber.

If only a part of the supply air from the pressure side of the pressurebooster is supplied to the supply air chamber, then the rest of thesupply air can be supplied advantageously from another hot air processof the fibrous web production.

It is an advantage in addition to provide, in particular in a supply airsupply line connected to the supply air chamber, a heat exchanger forincreasing the supply air temperature.

On a practical embodiment provision is made, in particular in a supplyair supply line connected to the supply air chamber, for an inparticular adjustable and/or controllable heating device for increasingthe supply air temperature.

The heating device can include in particular a gas burner, a gas turbineand/or the like.

It is an advantage in particular also to provide a water separator, inparticular a condensation device, in order to remove water from theexhaust air.

According to a practical embodiment of the inventive drying apparatus,the exhaust air chamber is formed by the suction box of a suction rollerand the supply air chamber by a hood assigned to said suction roller.

In this case the fibrous web can be passed, in particular together witha permeable structured belt, over the suction roller, whereby thefibrous web lies between the permeable structured belt and the suctionroller and the hot supply air flows out from the hood in successionthrough the permeable structured belt and the fibrous web into thesuction box of the suction roller.

The permeable structured belt and the fibrous web can be pressed in thiscase by way of a permeable press belt against the suction roller,whereby the hot supply air flows out from the hood in succession throughthe permeable press belt, the permeable structured belt and the fibrousweb into the suction box of the suction roller.

In addition, a dewatering belt can be passed around the suction rollersuch that said dewatering belt lies between the suction roller and thepermeable structured belt and the hot air flows through said dewateringbelt into the suction box of the suction roller.

According to another advantageous embodiment, the supply air supplied tothe supply air chamber can be taken partly from a hood which is assignedto a drying cylinder, in particular a Yankee cylinder, which togetherwith a press element forms a nip through which the fibrous web is passeddirectly after the suction roller.

In this case the hot air taken from the hood assigned to the dryingcylinder can be supplied in particular as supplementary air to apressure-side socket and/or a suction-side socket of the pressurebooster.

It is an advantage in particular also to provide at least one waterseparator in an exhaust air discharge line connected to the exhaust airchamber, in a suction-side socket of the pressure booster and/or in apressure-side socket of the pressure booster.

In this case the water separator is provided, looking in the flowdirection of the returned exhaust air, preferably upstream from theheating device for increasing the supply air temperature and/or upstreamfrom the point at which the hot air taken from the hood of the dryingcylinder is supplied.

The inventive machine for producing a fibrous web with athree-dimensional surface structure, in particular a paper web,paperboard web or tissue web, is characterized in that it is equippedwith an inventive drying apparatus, whereby the exhaust air chamber isformed by the suction box of a suction roller and the supply air chamberby a hood assigned to said suction roller and the fibrous web is passedtogether with a permeable structured belt over the suction roller, andwhereby the fibrous web lies between the permeable structured belt andthe suction roller and the hot supply air flows out from the hood insuccession through the permeable structured belt and the fibrous webinto the suction box of the roller.

On a practical embodiment of the inventive machine the permeablestructured belt and the fibrous web are pressed by way of a permeablepress belt against the suction roller, whereby the hot supply air flowsout from the hood in succession through the permeable press belt, thepermeable structured belt and the fibrous web into the suction box ofthe suction roller.

In addition, a dewatering belt can be passed around the suction rollersuch that said dewatering belt lies between the suction roller and thepermeable structured belt and the hot air flows through said dewateringbelt into the suction box of the suction roller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 shows a schematic representation of a machine for producing afibrous web with a three-dimensional surface structure, said machinehaving a drying apparatus including a hot air circuit; and

FIG. 2 shows a schematic cross-sectional representation of a blowerserving as a pressure booster.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention, and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown a schematic representation a machine 10 for producing a fibrousweb 12 with a three-dimensional surface structure, said machine beingequipped with an apparatus 14 including a hot air circuit for drying thefibrous web 12. The fibrous web 12 can be in particular a paper web,paperboard web or tissue web.

The drying apparatus 14 includes a suction roller 16 with a suction box18 forming an exhaust air chamber and a hood 20 assigned to the suctionroller 16 and forming a supply air chamber.

In this case the fibrous web 12 is passed together with a permeablestructured belt 22 over the suction roller 16, whereby the fibrous web12 lies between the permeable structured belt 22 and the suction roller16.

The permeable structured belt 22 and the fibrous web 12 are pressed forexample by way of a permeable press belt 24 against the suction roller16. In this case the hot air flows out from the hood 20 in successionthrough the permeable press belt 24, the permeable structured belt 22and the fibrous web 12 into the suction box 18 of the suction roller 16.

In addition, a dewatering belt 36 can be passed around the suctionroller 16 such that said dewatering belt 16 lies between the suctionroller 16 and the permeable structured belt 22 and the hot supply airflows through said dewatering belt into the suction box 18 of thesuction roller 16. Hence in the case in question, the supply air flowsin succession through the permeable press belt 24, the permeablestructured belt 22, the fibrous web 12 and the dewatering belt 36.

The machine includes in addition a former with two converging dewateringbelts 22, 26, whereby the inner belt in the case in questionsimultaneously forms the permeable structured belt 22. The twodewatering belts 22, 26 converge, thus forming a fiber intake nip 28,and are passed over a forming element 30 such as in particular a formingroller.

In the case in question the permeable structured belt 22 is thus formedby the inner dewatering belt of the former which comes into contact withthe forming element 30. The outer dewatering belt 26, which does notcome into contact with the forming element 30, is separated again fromthe fibrous web 12 and from the permeable structured belt 22 carryingsaid web directly after the forming element 30.

Fibrous suspension is fed by way of a headbox 32 into the fiber intakenip 28. Provided between the forming element 30 and the drying apparatus14 is a suction element 34 by way of which the fibrous web 12 is heldagainst the permeable structured belt 22 and pressed against saidpermeable structured belt 22.

Directly after the drying apparatus 14, the dewatering belt 36 isseparated again from the permeable structured belt 22 and the fibrousweb 12. In this case provision is made behind the drying apparatus 14for a pickup or separating element 38 by way of which the fibrous web 12is held against the permeable structured belt 22 during separation fromthe dewatering belt 36.

Directly afterwards, the fibrous web 12 is passed together with thepermeable structured belt 22 through a press nip 44 formed by a dryingcylinder 40, such as a Yankee cylinder, and a press element 42 such as apress roller. Behind said press nip 44, the permeable structured belt 22is separated again from the drying cylinder 40 while the fibrous web 12remains on the drying cylinder 40. A hood 46 is assigned to the dryingcylinder 40.

In addition, a spray tube 48 for coating or the like can be assigned tothe drying cylinder 40.

At least one so-called Uhle box 50 and/or at least one spray tube 52 canbe assigned to the permeable structured belt 22 and the dewatering belt36.

The apparatus 14 serves to dry the fibrous web 12 by way of hot air inthat the fibrous web 12 is charged with the supply air for the dryingfrom the hood 20 assigned to the suction roller 16. In this case,exhaust air arising during the drying operation passes into the suctionbox 18 of the suction roller 16. The exhaust air from the suction box 18is supplied at least partly to the suction side 54 of a pressure booster56. At least a part of the supply air from the pressure side 58 of thepressure booster 56 is then supplied to the hood 20 assigned to thesuction roller 16. A hot air circuit serving to dry the fibrous web 12is thus formed.

On the embodiment in question there is a type of through-flow dryingdevice on which the supply air chamber formed by the hood 20 and theexhaust air chamber formed by the suction box 18 are arranged onopposite sides of the fibrous web 12.

The pressure booster 56 can include for example at least one blowerwhich can have a single-stage or multi-stage construction.

If only a part of the supply air from the pressure side 58 of thepressure booster 56 or only a part of the air originating from thesuction box 18 forming the exhaust air chamber is supplied to the hood20 assigned to the suction roller 16, then the rest of the supply aircan be supplied from another hot air process of the fibrous webproduction.

Provision can be made, in particular in a supply air supply line 60connected to the hood 20, for a heat exchanger or an in particularadjustable and/or controllable heating device 62 for increasing thesupply air temperature. In the case in question, the heating device 62includes for example a burner, in particular a gas burner. The use offor example a gas turbine is also possible.

Provision can also be made in particular for a water separator 64, inparticular a condensation device, in order to remove water from theexhaust air. On the embodiment in question, such a water separator 64 isarranged in an exhaust air discharge line 66 connected to the suctionbox 18 of the suction roller 16. In principle it is also possible forsuch a water separator to be provided in a suction-side socket and/or ina pressure-side socket of the pressure booster 56.

As is evident from FIG. 1, it is possible on the embodiment in questionfor the supply air supplied to the hood 20 assigned to the suctionroller 16 also to be taken partly from the hood 46 assigned to thedrying cylinder 40.

In this case the hot air taken from the hood 46 assigned to the dryingcylinder 40 can be supplied in particular as supplementary air to apressure-side socket and/or the suction-side socket of the pressurebooster 56. Another pressure booster 70 can be arranged in therespective supply line 68 leading to the socket or sockets of thepressure booster 56. In this supply line 68 it is also possible toprovide in particular a filter 72 in addition to servo-valves or controlvalves.

As is evident from FIG. 1, it is also possible for a control valve 74 tobe arranged in the supply air supply line 60 between the pressurebooster 56 and the drying apparatus 14.

FIG. 2 shows in a schematic cross-sectional representation an exemplaryembodiment of the pressure booster 56, which here can be constructed asa single-stage blower I or as a multi-stage blower II.

In this case, said blower can be equipped expediently with connectionsQ_(Zi) for different vacuum levels.

On the exemplary embodiment in question, as it is shown in particular inFIG. 1, the hood 20 is assigned to the suction roller 16 at leastessentially in the region of the suction box 18. Said hood is suppliedwith hot and as far as possible dry supply air, which flows through thefibrous web 12 covered by the permeable or openly structured belt 22,which can be in particular a mesh, and is discharged again via thesuction box 18 as exhaust air. It has been discovered to be an advantagefor an efficient drying process if the air temperature is ≧100° C. Thisis important in particular when steam is used for heating the fibrousweb 12.

According to the invention, the hood supply air and the suction rollerexhaust air are now supplied at least partly in the circuit via thepressure booster 56. In this case the arrangement is selected such thaton the one hand the temperature increase caused through compression inthe pressure booster 56 is used for promoting the dewatering processwhile on the other hand the hot exhaust air is re-used.

To compensate air losses, supplementary air can be supplied into thepressure-side socket and/or the suction side socket of the pressurebooster 56.

Provision can also be made in particular for a condensation device inorder to remove water from the exhaust air.

Similarly, it is possible to use a heating device for the supply air inorder to have in particular a control possibility and/or an adjustmentpossibility for the air temperature.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

List of Reference Numerals

-   10 Machine-   12 Fibrous web-   14 Drying apparatus-   16 Suction roller-   18 Exhaust air chamber, suction box-   20 Supply air chamber, hood-   22 Permeable structured belt-   24 Permeable press belt-   26 Dewatering belt-   28 Fiber intake nip-   30 Forming element, forming roller-   32 Headbox-   34 Suction element-   36 Dewatering belt-   38 Pickup or separating element-   40 Drying cylinder, Yankee cylinder-   42 Press element-   44 Press nip-   46 Hood-   48 Spray tube-   50 Uhle box-   52 Spray tube-   54 Suction side-   56 Pressure booster-   58 Pressure side-   60 Supply air supply line-   62 Heating device-   64 Water separator-   66 Exhaust air discharge line-   68 Supply line-   70 Another pressure booster-   72 Filter-   74 Control valve

1. An apparatus for drying a web of fibrous material using hot air, saidapparatus comprising: a supply air chamber configured for supplying asupply air with which the web is charged for a drying operation; anexhaust air chamber configured for being that which an exhaust air fromsaid drying operation passes into; a pressure booster including asuction side and a pressure side, said exhaust air from said exhaust airchamber being supplied at least partly to said suction side of saidpressure booster, at least a part of said supply air being supplied tosaid supply air chamber coming from said pressure side of said pressurebooster; and a hood assigned to a drying cylinder arranged downstreamfrom said supply air chamber and said exhaust air chamber in a traveldirection of the web, said supply air supplied to said supply airchamber being taken partly from said hood assigned to said dryingcylinder.
 2. The apparatus according to claim 1, wherein the apparatusis an impingement drying device.
 3. The apparatus according to claim 2,wherein said supply air chamber and said exhaust air chamber arearranged on a same side of the web.
 4. The apparatus according to claim3, wherein said supply air chamber and said exhaust air chamber form ashared space.
 5. The apparatus according to claim 1, wherein theapparatus is a through-flow drying device.
 6. The apparatus according toclaim 5, wherein said supply air chamber and said exhaust air chamberare arranged on opposite sides of the web.
 7. The apparatus according toclaim 5, wherein a positive pressure in a range from approximately 0 toapproximately 0.5 bar exists in said supply air chamber.
 8. Theapparatus according to claim 5, wherein a positive pressure in a rangefrom approximately 0.002 to approximately 0.3 bar exists in said supplyair chamber.
 9. The apparatus according to claim 5, wherein a positivepressure ≧0.01 exists in said supply air chamber.
 10. The apparatusaccording to claim 5, wherein a positive pressure ≧0.02 exists in saidsupply air chamber.
 11. The apparatus according to claim 5, wherein apositive pressure ≧0.05 exists in said supply air chamber.
 12. Theapparatus according to claim 5, wherein a negative pressure in a rangefrom approximately 0 to approximately 0.8 bar exists in said exhaust airchamber.
 13. The apparatus according to claim 5, wherein a negativepressure in a range from approximately 0.2 to approximately 0.7 barexists in said exhaust air chamber.
 14. The apparatus according to theclaim 5, wherein a negative pressure in a range from approximately 0.4to approximately 0.7 bar exists in said exhaust air chamber.
 15. Theapparatus according to claim 1, wherein said pressure booster includesat least one blower.
 16. The apparatus according to claim 15, whereinsaid pressure booster includes at least one multi-stage blower.
 17. Theapparatus according to claim 15, wherein said pressure booster includesat least one single-stage blower.
 18. The apparatus according to claim15, wherein said pressure booster includes at least one radial blower.19. The apparatus according to claim 15, wherein said pressure boosterincludes at least one axial blower.
 20. The apparatus according to claim1, wherein a temperature of one of said supply air and a supply airfraction originating from said pressure booster is ≧100° C.
 21. Theapparatus according to claim 1, wherein a temperature of one of saidsupply air and a supply air fraction originating from said pressurebooster is ≧150° C.
 22. The apparatus according to claim 1, wherein atemperature of one of said supply air and a supply air fractionoriginating from said pressure booster is ≧200° C.
 23. The apparatusaccording to claim 1, wherein said supply air chamber is supplied withmore than 50% of said supply air from said pressure side of saidpressure booster.
 24. The apparatus according to claim 23, wherein atleast essentially 100% of said supply air from said pressure side ofsaid pressure booster is supplied to said supply air chamber.
 25. Theapparatus according to claim 1, wherein said supply air chamber issupplied with more than 60% of said supply air from said pressure sideof said pressure booster.
 26. The apparatus according to claim 1,wherein said supply air chamber is supplied with more than 70% of saidsupply air from said pressure side of said pressure booster.
 27. Theapparatus according to claim 1, wherein said supply air chamber issupplied with more than 80% of said supply air from said pressure sideof said pressure booster.
 28. The apparatus according to claim 1,wherein only a part of said supply air from said pressure side of saidpressure booster is supplied to said supply air chamber, the rest ofsaid supply air supplied to said supply air chamber being supplied fromanother hot air process used to produce the web.
 29. The apparatusaccording to claim 1, further including a supply air supply line,connected to said supply air chamber, and a heat exchanger forincreasing a temperature of said supply air.
 30. The apparatus accordingto claim 1, further including a supply air supply line, connected tosaid supply air chamber, and at least one of an adjustable andcontrollable heating device for increasing a temperature of said supplyair.
 31. The apparatus according to claim 30, wherein said heatingdevice includes a gas burner.
 32. The apparatus according to claim 30,wherein said heating device includes a gas turbine.
 33. The apparatusaccording to claim 1, further including a water separator for removingwater from said exhaust air.
 34. The apparatus according to claim 33,wherein said water separator is a condensation device.
 35. The apparatusaccording to claim 1, further including a suction roller including asuction box, said exhaust air chamber including said suction box, saidsupply air chamber including a hood assigned to said suction roller. 36.The apparatus according to claim 35, further including a permeablestructured belt, the web being passed together with said permeablestructured belt over said suction roller, the web lying between saidpermeable structured belt and said suction roller, a hot said supply airflowing out from said hood assigned to said suction roller in successionthrough said permeable structured belt and the web into said suction boxof said suction roller.
 37. The apparatus according to claim 36, furtherincluding a permeable press belt which presses said permeable structuredbelt and the web against said suction roller, said hot supply airflowing out from said hood assigned to said suction roller in successionthrough said permeable press belt, said permeable structured belt, andthe web into said suction box of said suction roller.
 38. The apparatusaccording to claim 37, further including a dewatering belt which ispassed around said suction roller such that said dewatering belt liesbetween said suction roller and said permeable structured belt and saidhot supply air flows through said dewatering belt into said suction boxof said suction roller.
 39. The apparatus according to claim 35, whereinsaid drying cylinder together with a press element forms a press nipthrough which the web is passed directly after said suction roller. 40.The apparatus according to claim 39, wherein said drying cylinder is aYankee cylinder.
 41. The apparatus according to claim 39, wherein saidpressure booster includes at least one of a pressure-side socket and asuction-side socket, a hot air taken from said hood assigned to saiddrying cylinder being supplied as supplementary air to said at least oneof said pressure-side socket and said suction-side socket of saidpressure booster.
 42. The apparatus according to claim 41, furtherincluding an exhaust air discharge line connected to said exhaust airchamber and at least one water separator at least one of in said exhaustair discharge line and in at least one of said suction-side socket ofsaid pressure booster and said pressure-side socket of said pressurebooster.
 43. The apparatus according to claim 42, further including aheating device for increasing a temperature of said supply air, theapparatus being configured for taking said hot air from said hood ofsaid drying cylinder, said water separator being provided, looking in aflow direction of a returned said exhaust air, at least one of upstreamfrom said heating device and upstream from a point at which said hot airtaken from said hood of said drying cylinder is supplied.
 44. A machinefor producing a web of fibrous material with a three-dimensional surfacestructure, said machine comprising: a drying apparatus for drying theweb using hot air, said drying apparatus including: a supply air chamberconfigured for supplying a supply air with which the web is charged fora drying operation; an exhaust air chamber configured for being thatwhich an exhaust air from said drying operation passes into; a pressurebooster including a suction side and a pressure side, said exhaust airfrom said exhaust air chamber being supplied at least partly to saidsuction side of said pressure booster, at least a part of said supplyair being supplied to said supply air chamber coming from said pressureside of said pressure booster; a suction roller including a suction box,said exhaust air chamber including said suction box, said supply airchamber including a hood assigned to said suction roller; and apermeable structured belt, the web being passed together with saidpermeable structured belt over said suction roller, the web lyingbetween said permeable structured belt and said suction roller, a hotsaid supply air flowing out from said hood in succession through saidpermeable structured belt and the web into said suction box of saidsuction roller.
 45. The machine according to claim 44, wherein saiddrying apparatus includes a permeable press belt, said permeablestructured belt and the web being pressed by said permeable press beltagainst said suction roller, said hot supply air flowing out from saidhood in succession through said permeable press belt, said permeablestructured belt, and the web into said suction box of said suctionroller.
 46. The machine according to claim 45, said drying apparatusfurther including a dewatering belt which is passed around said suctionroller such that said dewatering belt lies between said suction rollerand said permeable structured belt and said hot supply air flows throughsaid dewatering belt into said suction box of said suction roller.